In a half-duplex conferencing model, such as Push-to-talk over Cellular (PoC), at any given time only one person will be given the right to talk and others shall be in a listening mode. Each member explicitly requests the “Right-to-talk” in a given floor, and a PoC server arbitrates the requests and grants the floor based on certain rules. This mechanism of requesting, arbitrating and granting the Right-to-communicate is called the Floor control or Media Burst control. In order for the PoC architecture to address the multimedia requirements and use-cases specified in the PoC specification, the architecture supports a flexible floor control scheme that supports multiple floors for multiple media in a session, one floor for one or more media in a session, and grouping floors and media together.
The PoC architecture supports half-duplex conferencing using a SIP/IP core architecture, such as “walkie-talkie” like voice communication for person-to-person and group call scenarios. The PoC specification supports an extensible architecture to support continuous media, such as voice and video. In particular, the PoC specification includes a Real Time Protocol (RTP) for carrying continuous media and a Real Time Control Protocol (RTCP) for controlling and managing the flow of continuous media. RTCP was extended to support floor control functionality for PoC by embedding the floor control details in the RTCP APP specific messages. RTP/RTCP protocols were primarily engineered with the focus to support continuous media, and it currently utilizes the unreliable transport protocol UDP for voice. This introduces a potential bottle neck to transferring reliably discrete content, such as still images, text and data using the existing PoC architecture.
This is not the case for discrete media, such as still images and text. The PoC specification includes a Message Session Relay Protocol (MSRP) for carrying discrete media, but does not have any means for controlling the transfer of discrete media. MSRP is full-duplex, so it lacks floor control and content flow control schemes required for certain applications. With a focus to minimize effort, optimize mobile resources and avoid re-inventing solutions, it is preferable to reuse the protocols across different enablers. The MSRP protocol currently lacks the ability to support the half-duplex communication model and, in particular, lack the ability to enable floor control functionality to support half-duplex communication, like PoC.
Accordingly, there is a need for a protocol for half-duplex communication that provides a control mechanism for discrete media transfer by MSRP.